An ultrasonic non-invasive surgery has advantages of low risk, few side effects and allowing the patient to leave the hospital quickly afterward, and has been widely used in various medical fields. In order to expand the application scope of the ultrasonic non-invasive surgery, for example, being applied to the medical fields of micro-tissues such as cardiovascular surgery, ophthalmology or invasive sound therapy, a high-frequency and high-resolution ultrasonic array is under development.
In recently years, international research and development units introduce a Piezoelectric Micromachined Ultrasound Transducer (pMUTs) (referred to as pMUTs technology in the following) having high precision and wafer-level volume production. The pMUTs technology deposits a thin-film piezoelectric material (several μms) on a silicon substrate, and then defines an ultrasonic transducer element having an empty back-cavity through lithography, development and etching processes.
The current pMUTs technology uses a plane dimension defining the ultrasonic transducer element to obtain a flexure mode to determine an operating frequency of the piezoelectric ultrasonic detector. In practical application, many ultrasonic transducer units are usually gathered and arranged into an ultrasonic transducer array having a unit space between adjacent units. However, according to the above design, the unit space of the ultrasonic transducer array is usually greater than ½ wavelength of the operating frequency, and when the unit space is greater than ½ wavelength of the environment under test, a grating lobe effect as shown in FIGS. 1A and 1B is caused. To form an image of 0 degree, wrong reflection information with angles θ1 and θ−1 are thus generated, resulting in wrong radiography, and a real image of the object to be tested cannot be reliably obtained.